Laminated metal sprockets have been known in the U.S. patented art for driving metal chains or conveyors. Thus, T. C. Luce in U.S. Pat. No. 1,201,748, Oct. 17, 1916 for Sprocket Driving Device discloses a chain drive sprocket formed of three disc like sprocket laminations riveted together with paper sheets therebetween to reduce noise. Circumferentially extending sprocket teeth are staggered in such a way that alternating pairs of drive teeth are disposed on opposite sides of the sprocket.
K. F. J. Kirsten in U.S. Pat. No. 1,835,406, Dec. 8, 1931 for Power Transmitting Mechanism discloses a laminated metal sprocket driver for metal chain belts, wherein the laminations have openings to reduce the weight and material present in the sprocket. Different laminations are sandwiched with offset sprocket teeth, wherein the openings are also offset in such a way that the inner aperture surface of the sprocket is rough and uneven.
A metallic drag chain sprocket, shown in the E. J. Horkey, et al. U.S. Pat. No. 4,308,019, Dec. 29, 1981 for Drag Chain Sprocket is formed of spaced disc-like members welded coaxially along a cylindrical hub to support crossbar drive teeth. The discs are apertured to reduce weight and to form escape ports for abrasive material that might accumulate between the hub and the chain.
None of this prior art addresses the problems involved with driving plastic belts with metal sprocket teeth, particularly for operation in abrasive environment conditions or those which might tend to contaminate or erode the drive system. While some types of plastic to metal surfaces provide desirably low interface friction and good wear possibilities, this hybrid type of driving system creates significant problems when encountering abrasive conditions or contaminants that erode metal. It is therefore one objective of the invention to provide metal sprocket drives for plastic modular conveyor belts that overcome the presence of abrasives and resolve problems of working in sanitary conditions or with materials such as corrosives that tend to erode the metal. It is particularly necessary to provide conveyor belt systems that are suitable for use in sanitary environments, such as those dealing with sterile goods or foods.
Laminated sprocket drive systems have not heretofore been suitable for use in abrasive, corrosive or sanitary environments because of the existence of rough and hidden surface areas that cannot be sanitized and that tend to accumulate abrasives or corrosives that accelerate pitting and wear of metal parts to the extent that they accelerate wear and thus are not suitable for long life driving engagement with plastic modular belt drive surfaces.
It is therefore a general objective of the invention to improve the operation of conveyor belts and conveyor belt systems, particularly in abrasive, corrosive and sanitary environmental conditions.
A further objective of the invention is to correct the deficiencies of the prior art laminar sprocket drive systems such as those hereinbefore mentioned.
Further objects, features and advantages of the invention will be recognized throughout the following description, drawings and claims.